1. Field of the Invention
This invention relates to an improved roof support system for a mine or the like, and more specifically, to such a roof support system which utilizes a horizontal, transverse reinforcing member which is simple to provide and conveniently utilized to produce a desired tension between a pair of roof plates of the roof support system.
2. Description of the Prior Art
Although there are numerous methods for supporting the roof of mines, openings, or the like, one type which is commonly employed includes a roof truss structure which generally includes two inclined cords and a horizontal cord. The inclined cords are usually mine roof bolts or the like which extend into holes in the mine roof at about a 45.degree. angle. The mine roof bolts may be anchored in the inclined holes in the roof by well known means such as expansion shells and/or resin bonding. The horizontal cord or tie member extends transversely across the roof the mine between the terminal ends of the inclined cords located at the surface of the roof. Providing means for applying tension to the anchored, inclined cords and the horizontal cords can result in sufficient upward force being generated on the roof to allow safe operation in the mine or the like while preventing uncontrolled vertical downward movement of the roof or any other creeping movement thereof which might cause it to become unstable.
U.S. Pat. No. 2,667,037 disclosed a general roof support system which basically provides the type of upward forces described hereinabove. Specifically, a horizontal beam or the like was positioned transversely of the mine opening across the roof and was retained in place by a plurality of inclined bolts which anchored the horizontal beam and provided overall integrity for roof support.
U.S. Pat. No. 3,427,811 disclosed a system which provided for the same type of upward forces to support a mine roof but included the additional feature of a means for varying the tension on the horizontal cord and reportedly resulted in an overall system which exerted at least approximately equal tension on the horizontal cord and the inclined anchoring cords. Although U.S. Pat. No. 3,505,824, and 3,509,726 disclose roof support trusses or systems which function generally like that mentioned hereinabove, they employ different elements to create a combined tension on the inclined cord and horizontal cord components.
The roof support system generally disclosed in U.S. Pat. No. 4,395,161 results in a similar configuration but includes features for ease of installation and adjustability which may exist in the prior art devices mentioned hereinabove but are not as clearly demonstrated. Specifically, the device includes a pair of transition plates to be installed in the roof of the mine by inclined cords in the form of mine roof bolts which can be separately installed and adjusted to provide the desired tension thereto. Subsequently, the same or a different mining crew is then capable of installing a horizontal, transversely extending reinforcing member to provide the horizontal cord component of the mine roof truss. In the case of U.S. Pat. No. 4,395,161, the reinforcing member is disclosed to preferably be an elongated rod having threaded ends with adjusting nuts installed at each of the ends to produce tension between the transition plates.
When trying to determine which truss system or other roof support system should be utilized, there are some mine operating conditions and safety requirements which should be taken into consideration. A more attractive roof support system would be one which could reduce installation time to mining cycle time, included a means to provide uniform truss tensioning during installation with a capability to vary tensioning depending upon roof conditions and would improve the overall work conditions. These objectives were founded on the need to increase the effectiveness of the truss in roof support and reduce the cost of roof control. It is well known that roof control effectiveness can be enhanced by quickly supporting the roof after coal extraction. By installing the truss in the mining cycle, the time that the roof remains unsupported by the truss is decreased. By tensioning uniformly, a way is open for the truss to become the primary roof control method, thus reducing the requirement in many cases for roof bolting and trussing in the same location.
Further, it has been found that proper truss tensioning improves system effectiveness. Using a pipewrench as a tensioning tool has shown considerable variability in truss tensioning during installation and tensioning is dependent upon the size and strength of the operator and the time of day in which the truss is installed. For example, early in a work shift, trusses are usually installed with proper tensioning, but as the day wears on the quality of workmanship declines as in many other industries.
Truss tensioning is an unpopular task because conditions in some mining areas create an unnatural strenuous working position for the individual actually tensioning the truss. To gain a greater acceptance of this operation, any improvement in such a system which could reduce the installation time, reduce the strenuous nature of the work and eliminate the potential for straintype of injuries would be desirable.
Accordingly, while the device shown in U.S. Pat. No. 4,395,161 incorporates separate installation of a roof plate with a separately adjustable inclined mine roof bolt, any improvement to the horizontal, transversely extending reinforcing member would be desirable. Further, it would clearly be an advantage if a more simplified means were available for installing such a horizontal, transverse reinforcing member which method also facilitated the use of power tools for creating the desired tension between the roof plates.